High power density insulated exhaust heating system

ABSTRACT

An exhaust gas heating unit for an engine includes a housing and a heating element. The housing includes a tubular peripheral wall and has an interior hollow space. The heating element has first and second ends and extends longitudinally therebetween to form a spiral shape within the interior hollow space. The heating element includes a thermally conductive sheath, an electrically conductive resistance element that extends longitudinally within the external sheath, and an electrically insulating material disposed about the resistance element between the resistance element and the sheath. A heat transfer member is positioned within the interior hollow space and is formed from one or more strips of thermally conductive material. The strips contact the external sheath at a plurality of locations between the first end and the second end. The heat transfer member has a corrugated shape that follows the spiral shape of the heating element.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/535,096, filed on Nov. 24, 2021, which is a continuation ofU.S. patent application Ser. No. 17/411,352, filed on Aug. 25, 2021,which is a continuation of U.S. patent application Ser. No. 16/806,175,filed on Mar. 2, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/448,200, filed on Mar. 2, 2017, which claims thebenefit of U.S. Provisional Application No. 62/415,042, filed Oct. 31,2016, entitled “High Power Density Insulated Exhaust Heating System.”The disclosures of the above applications are incorporated herein byreference in their entireties.

FIELD

The present disclosure relates to exhaust systems for internalcombustion engines, and more specifically to exhaust gas heatingapparatuses installed in the exhaust systems.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Heater systems are used in exhaust systems that are coupled to aninternal combustion engine in order to assist in the reduction of theundesirable release of various gases and other pollutant emissions intothe atmosphere. These exhaust systems typically include variousafter-treatment devices, such as diesel particulate filters (DPF); acatalytic converter; selective catalytic reducers (SCR) that capturecarbon monoxide (CO), nitrogen oxides (NO_(x)), particulate matters(PMs), and unburned hydrocarbons (HCs) contained in the exhaust gas; adiesel oxidation catalyst (DOC); a lean NO_(x) trap (LNT); an ammoniaslip catalyst; or reformers, among others. The heaters may be activatedperiodically or at a predetermined time to increase the exhausttemperature and activate the catalysts and/or to burn the particulatematters or unburned hydrocarbons that have been captured in the exhaustsystem.

The electric heaters are generally installed in exhaust pipes orcomponents such as containers of the exhaust system and are subjected toharsh environmental conditions, such as vibration, mechanical shock,temperature cycling, high heat, etc.

SUMMARY

In one form, a heating apparatus for an exhaust gas system having acontainer body is provided. The heating apparatus includes at least oneheater element, and a support member disposed inside the container bodyfor restricting movement of the at least one heating element in thecontainer body. The support member defines a tortuous geometry andflanks opposed sides of the at least one heater element and thus isarranged to increase heat transfer from the at least one heater elementto an exhaust gas flowing through the container body.

In another form, a heating apparatus for an exhaust gas system isprovided. The heating apparatus includes an outer peripheral walldefining a tubular shape and having a hollow space, at least one heaterelement disposed in the hollow space, and a plurality of fins attachedto the at least one heater element to transfer heat from the at leastone heater element to an exhaust gas that flows through the hollow spaceof the outer peripheral wall.

In still another form, a heating apparatus for an exhaust gas system isprovided. The heating apparatus includes an outer peripheral wall havinga tubular shape and defining a hollow space, a heater element disposedin the hollow space, and a strip member. The heater element includes aplurality of sections arranged along a radial direction of the outerperipheral wall. The strip member includes a plurality of sectionsdisposed between adjacent two of the sections of the heater element andbetween an outermost section of the heater element and the outerperipheral wall. The strip member secures the heater element to theouter peripheral wall and increases heat transfer from the heaterelement to an exhaust gas flowing through the hollow space.

In yet another form, a heating apparatus for a fluid flow system havinga fluid conduit is provided that comprises at least one heater elementand a support member disposed within the fluid conduit and configuredfor restricting movement of the at least one heater element relative tothe fluid conduit. The support member defines a tortuous geometry andflanks opposed sides of the at least one heater element along a majorityof a length of the at least one heater element, and the support memberincreases heat transfer from the at least one heater element to a fluidflowing through the fluid conduit.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a perspective view of a heating apparatus constructedaccording to the teachings of the present disclosure;

FIG. 2 is another perspective view of a heating apparatus of FIG. 1,wherein the heating apparatus is shown to be in the fluid flow channel;

FIG. 3 is a cross-sectional view of a heater element of FIG. 2;

FIG. 4 is a cross-sectional view of a tubular heater element constructedin accordance with the teachings of the present disclosure;

FIG. 5 is a schematic perspective view of another heating apparatusconstructed in accordance with the teachings of the present disclosure;

FIG. 6 is a schematic cross-sectional view of a heater element of theheating apparatus of FIG. 5;

FIG. 7 is a perspective view of still another heating apparatusconstructed in accordance with the teachings of the present disclosure;

FIG. 8 is a perspective view of still another heating apparatusconstructed in accordance with the teachings of the present disclosure;

FIG. 9 is a perspective view of a corrugated strip of the heatingapparatus of FIG. 8, wherein the corrugated strip is shown in itsoriginal, unbent state;

FIG. 10 is a perspective view of an outer peripheral wall of the heatingapparatus of FIG. 8;

FIG. 11 is a perspective cross-sectional view of a section of the outerperipheral wall of FIG. 10; and

FIG. 12 is a perspective view of still another form of a heatingapparatus constructed in accordance with the teachings of the presentdisclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Referring to FIG. 1, the heating apparatus 1 in one form generallyincludes a junction box 5, a perforated box assembly 10, a containerbody 14 including one or more separable container section components 15,and a heater flange component 20. Exhaust system coupling components 25may be provided at opposing ends of the container body 14 to couple theheating apparatus 1 into an exhaust system (not shown). The flow ofexhaust gases passes from the exhaust system into the heating apparatus1 through an exhaust gas channel 29 formed in the heating apparatus 1.The exhaust gas channel 29 is defined jointly by the container body 14and the heater flange component 20 and extends along an exhaust flowdirection Z of the container body 14. The heater flange component 20generally has a plate configuration in one form and may include aplurality of tabs 21 that are inserted into corresponding slots 23 inthe container body 14. The modular design of the heating apparatus 1allows the dimensions of the various components in the heating apparatus1 to stay the same with only the length of each component being variedto accommodate the requirement(s) of the application. A junction box lid7 may be incorporated into the heating apparatus 1.

Alternatively, the container body 14 and the heater flange component 20may be configured to fit inside an exhaust pipe (not shown) such thatthe container body 14 is disposed in an exhaust gas channel defined bythe exhaust pipe.

In other forms of the present disclosure, alternate heater arrangementscan be provided without the junction box 5 and the perforated boxassembly 10, such as those described in greater detail below. Therefore,it should be understood that the junction box 5 and the perforated boxassembly 10 are merely exemplary and should not be construed as limitingthe scope of the present disclosure.

Referring to FIG. 2, the heating apparatus 1 includes one or more heaterelements 12 and a support member 16. The heater elements 12 may bedisposed to be in a direction across the exhaust flow direction Z. Forexample, the heater elements 12 may be a plurality of cartridge heatersextending along a vertical direction Y, perpendicular to the exhaustflow direction Z. Alternatively, the heater elements 12 may be disposedto be at an angle relative to the exhaust flow direction Z. In FIG. 2,the junction box 5 and the junction box lid 7 are removed to showproximal ends 30 and the power pins 40 of the heater elements 12.

Referring to FIGS. 3 and 4, the heater elements 12 may be cartridgeheaters, each including a resistive heating element 22 in the form of ametal wire, a core 28 around which the resistive heating element 22 iswound, an outer sheath 60 surrounding the core 28, and an insulatingmaterial 64. The core 28 may be a ceramic core defining two longitudinalbores 34, 36 in which a pair of power pins 40 inserted. A first end 50of the resistive heating element 22 is electrically connected to one ofthe power pins 40 and the other end 52 of the resistive heating element22 is electrically connected to the other one of the power pins 40. Theouter sheath 60 may have an open end and a closed end, or two open ends,thus creating an annular space between the outer sheath 60 and theresistive heating element 22. The insulating material 64 fills in theannular space and may be any material that can provide electricalisolation between the resistive heating element 22 and the outer sheath60. As an example, the insulating material 64 may be magnesium oxide(MgO) or the like and is poured into the open end of the sheath 60 tofill the annular space between the resistive heating element 22 and theinner surface of the sheath 60.

The open end of the sheath 60 may be sealed, for example by using apotting compound and/or discrete sealing members 62. The entire assemblyis then compacted or compressed, as by swaging or by other suitableprocesses, to reduce the diameter of the outer sheath 60 and to thuscompact and compress the MgO and to at least partially crush the ceramiccore 28 so as to collapse the core 28 about the power pins 40 to ensuregood electrical contact and thermal transfer. The compacted MgO providesa relatively good heat transfer path between the resistive heatingelement 22 and the outer sheath 60 and it also electrically insulatesthe outer sheath 60 from the resistive heating element 22. The heaterelement 12 defines a proximal end 30 where the sealing member 62 isdisposed and the power pins 40 protrudes outwardly, and a distal end 32opposing the proximal end 30.

Various constructions and further structural and electrical details ofcartridge heaters are set forth in greater detail in U.S. Pat. Nos.2,831,951 and 3,970,822, which are commonly assigned with the presentapplication and the contents of which are incorporated herein byreference in their entirety. Therefore, it should be understood that theform illustrated herein is merely exemplary and should not be construedas limiting the scope of the present disclosure.

Referring back to FIG. 2, the heater elements 12 are disposed such thatthe distal ends 32 extend into the exhaust gas channel 29 and theproximal ends 30 and the power pins 40 extend through the perforated boxassembly 10 and into the junction box 7. The support member 16 includesa plurality of support sheets 18 parallel to one another and extendingalong a horizontal direction X perpendicular to the exhaust flowdirection Z and the vertical direction Y to support the plurality of theheater elements 12 in the container body 14. The plurality of supportsheets 18 may be spaced apart along the vertical direction Y at aspacing less than 3 inches. Optionally, the support member 16 furtherincludes at least one cross member 19 extending in a vertical directionY for connecting the support sheets 18. The support sheets 18 and thecross member 19 may be formed as an integral, one-piece component, ormay be formed separately and later connected together. Alternatively,the support member 16 may include only one support sheet 18 to supportthe heating elements 12 inside the exhaust gas channel 29 whiledistributing the heat generated by the heater elements 12 to the exhaustgas flowing in the exhaust gas channel 29. The support member 16 mayprovide a combination of conductive, convective and radiative heattransfer to improve heat transfer from the heater elements 12 to thesurrounding exhaust gas, thereby obtaining, without increasing thetemperature of the heater, a higher power density than that obtained bya heater element without the support member 16.

Power density is determined by dividing the power by the surface area.For a heater element of a type of a cartridge heater, a cable heater ora tubular heater, the surface area may be the sheath surface area or theresistive wire surface area. The maximum power density of the heater toavoid overheating is also affected by velocity of the exhaust gas,which, in turn, is affected by the engine speeds and the engine loads.When the velocity of the exhaust gas is higher, more heat from theheater element may be carried away by the exhaust gas per unit of time.Therefore, the heater element may generate a higher power density whenthe velocity of the exhaust gas is relatively high without overheatingor damaging the heater element. While it is desirable to provide aheater element with increased power density to reduced size and weightof the heater element, the power density of the heater element may belimited when an engine is running at a lower engine speed and at lowerengine load. When the velocity of the exhaust gas flow is relatively lowdue to lower engine speed and lower engine load, less heat is carriedaway by the exhaust gas per unit of time. The heater element heats upfaster, and thus a lower watt density is used in order to avoidoverheating. The durability of a heater element of a cartridge type, acable type, or a tubular type depends, in part, on the temperature ofthe resistive heating element and the outer sheath. Therefore, theheater element should be configured based on the engine speed and theengine torque in order to properly heat the exhaust gas withoutcompromising durability of the heater element.

For example, for a 7-liter engine running in a low idle condition, themass flow could be about 0.04 kg/s, and the exhaust temperatureapproximately 150° C. A typical single element heater in these exhaustconditions may allow a maximum power density of approximately 50watts/in² for the sheath and approximately 120 watts/in² for theresistive heating wire in order to avoid damage to the heater.

In contrast, under the similar engine operating conditions, the heatingapparatus including the heater element and the support member accordingto the present disclosure may allow a maximum power density ofapproximately 84 watts/in² for the sheath and approximately 230watts/in² for the resistance wire and result in the same heatertemperature and durability. Therefore, the heating apparatus of thepresent disclosure enable higher power density than that of a typicalheater element.

Therefore, the support member of the heating apparatus of the presentdisclosure not only stiffens or restricts the movement of the insulatedheater element, but also improves heat transfer from the heater elementto the surrounding exhaust gas. Therefore, the power density of theheating apparatus can be increased without increasing the target heatingtemperature of the heater element.

Alternatively, the heater elements 12 may be securely disposed insidethe the exhaust gas channel 29, for example, by perforated box assembly10 and/or other mounting structure provided at the proximal ends 32 ofthe heater elements 12. In this case, restricting movement of the heaterelement 12 by a support member may not be necessary. Therefore, theheating apparatus 1 may include one or more fins attached to the heaterelement 12 for the sole purpose of providing conductive, convective andradiative heat transfer to improve heat transfer from the heater element12 to the surrounding exhaust gas. The fins may be configured to bestructurally similar to the support sheets 18 as shown in FIG. 2, butare not used to support the heater elements 12.

Referring to FIG. 5, another form of a heating apparatus 70 may includea heater element 72 and a support member 74. The heater element 72 maybe a cable heater and bent into a tortuous shape such as those selectedfrom a group consisting of a spiral shape, a sinuated shape, a coilshape, a zig-zag shape or any of the combinations thereof. The supportmember 74 may include a corrugated strip 74 and a peripheral wall 76surrounding the corrugated strip 74. In the illustrative example of FIG.5, the corrugated strip 74 is bent into a spiral shape conforming to thespiral shape of the heater element 72 such that heater element 72 may besandwiched between portions of the corrugated strip 74. In other words,the heater element 72 includes a plurality of sections arranged along aradial direction of the peripheral wall 76 which has a tubular shape andwhich defines a hollow space. The corrugated strip 74 incudes aplurality of sections disposed between adjacent two of the sections ofthe heater element 72 and between an outermost section of the heaterelement 72 and the peripheral wall 76. Optionally, the corrugated strip74 may be wrapped back to have some overlap portions A. Shapes otherthan the spiral shape may also be employed, such as by way of example,sinuated bends (not shown) while remaining within the scope of thepresent disclosure.

The corrugated strip 74 includes alternate ridges 80 and grooves 82. Thecorrugated strip 74 may be brazed or welded to the heater element 72 ata plurality of contact points to increase stiffness of the heaterelement 72. The plurality of contact points are spaced at a spacingalong a length of the corrugated strip 74. The spacing is less than tentimes an outerside diameter of the heater element 72. The naturalfrequency of vibration for the sections of the heater element betweenadjacent two contact points may be greater than 400 Hz. When thecorrugated strip 74 and the heater element 72 have fewer contact points,the heat transfer characteristics may be restricted, but it isrelatively easier to secure the heater element 72 to the corrugatedstrip 74. In contrast, when the corrugated strip 74 and the heater 72have more contact points, the heater transfer characteristics areoptimized but it is relatively difficult to secure the heater element 72to the corrugated strip 74. The number of the contact points is selectedsuch that a temperature variation across the heating apparatus is lessthan 200° C.

Alternately, the heater element 72 may be disposed loosely betweenportions of the corrugated strip 74, or not even contact the heaterelement 72. In either case, the corrugated strip 74 acts as both astiffener and a vibration dampener. The outer wall 72 may be a part ofthe container body 14 or a separate component from the container body 14and completely disposed in the exhaust gas channel.

Like the support sheets 18 in FIG. 2, the corrugated strip 74 provides acombination of conductive, convective and radiative heat transfer thatimproves heater transfer from the heater element 72 to the surroundingexhaust gas, thereby achieving a higher power density without increasingthe temperature of the heater element than that provided by a typicalheater element.

Referring to FIG. 6, the heater element 72 may be a cable heaterincluding a resistive heating element 84, an outer sheath 86, and aninsulating material 88 filling in a space between the resistive heatingelement 84 and the outer sheath 86. It is understood that the heaterelement 72 may be a cartridge heater, a tubular heater, or any heaterthat can be bent into a desired shape.

Referring to FIG. 7, another form of a heating apparatus 90 is shown toinclude a heater element 92 and a support member 94. The support member94 includes a corrugated sheet 96 wrapped into a spiral shape, and anouter peripheral wall 98 surrounding the corrugated sheet 96. Thecorrugated sheet 96 may be bent into a spiral shape conforming to thespiral shape of the heater element 92 so that the heater element 92 issandwiched between portions of the corrugated sheet 94. In this form,the use of a junction box and perforated box assembly is eliminated andthus a simpler and lower cost assembly is provided.

Referring to FIG. 8, another form of the heating apparatus is similar tothat of FIG. 5 except for the structure of the support member. Morespecifically, the heating apparatus 100 includes a heater element 102and a support member 104, which may be welded or brazed for joining. Thesupport member 104 includes a corrugated strip 106 and an outerperipheral wall 108. Similar to the corrugated strip 74 of FIG. 5, thecorrugated strip 106 is bent into a spiral shape conforming to thespiral shape of the heater element 102 and includes a plurality ofridges 110 and grooves 112. The outermost portion of the corrugatedstrip 106 is welded to an inner surface of the outer peripheral wall 108at the ridges 110. The outer peripheral wall 108 may be a part of thecontainer body 14 and defines the exhaust gas channel 29 or may becomponent separate from the container body 14. The outer peripheral wall108 may be loosely disposed inside the container body 14 or fixed to thecontainer body 14.

Referring to FIG. 9, the corrugated strip 106 is shown to be in anoriginal, unbent state. The corrugated strip 106 further defines aplurality of indentations 114 at the ridges 110 and grooves 112 tofacilitate engagement between the heater element 102 and the corrugatedstrip 106. Portions of the heater element 102 corresponding to theindentations 114 may be inserted into the indentations 114 to improveengagement between the heater element 102 and the corrugated strip 106.Although one row of indentations 114 is illustrated, it should beunderstood that multiple rows of indentations may be employed whileremaining within the scope of the present disclosure.

Referring to FIGS. 10 and 11, the outer peripheral wall 108 may define amounting feature for mounting the corrugated strip 106 onto the outerperipheral wall 108. For example, the mounting feature may be aplurality of annular grooves 118 formed on an inner surface of the outerperipheral wall 108 to facilitate engagement between the corrugatedstrip 106 and the outer peripheral wall 108. It is understood that themounting feature is not limited to the annular grooves 118 shown inFIGS. 10 and 11, and may be any structure that can engage and secure thecorrugated strip 106 to the outer peripheral wall 108.

Referring to FIG. 12, another form of a heating apparatus 120constructed in accordance with the teachings of the present disclosureis structurally similar to that of FIG. 5 except that the heatingapparatus 120 has a smaller size to fit in any part of theafter-treatment container or component to heat the exhaust gas, whilegenerating the same amount or close to the amount of heat generated by alarger size of the heating apparatus.

More specifically, the heating apparatus 120 includes a heater element122, and a support member 124. The support member 124, which may be asingle component or an assembly of pieces, includes a corrugated strip126, and a peripheral wall 128 surrounding the corrugated strip 126. Thesupport member 124 defines a tortuous geometry and in one form flanksopposed sides of the heater element 122 along a majority of a length ofthe heater element 122 as shown. As used herein, the term “tortuous”should be construed to mean a shape that changes direction a pluralityof times, in a regular or irregular manner, in order to increase heattransfer from the heater element 122 to the fluid flow, e.g. exhaustflow.

The heater element 122 may be formed into a tortuous shape selected froma group consisting of a spiral shape, a sinuated shape, a coil shape, azig-zag shape or any of the combinations thereof. To increase the totalamount of heat generated by the small-size heating apparatus 120, theheater element 122 is formed into more turns and is more compact. Thecorrugated strip 126 can be formed into more turns and includesalternate ridges 130 and grooves 132 to form a tortuous geometry. Thecorrugated strip 126 may be brazed, welded, or secured by any means tothe heater element 122 at the alternate ridges 130 and grooves 132. Dueto the reduced space defined between adjacent sections of the heaterelement 122, the corrugated strip 126 may be configured to form a wavysurface 134 between adjacent ridges 130 and grooves 132, and/or theridges 130 and the grooves 132 may be configured to have a wider contactarea with the adjacent sections of the heater element 122. As a result,the total surface area of the corrugated strip 126 may be furtherincreased to increase the heat transfer from the heater element 122 tothe surrounding exhaust gas.

Optionally, the heating apparatus 120 may further include one or morespacers 136 and an end piece 138. The spacer 136 may be used to fill anygap that may be present between the peripheral wall 128 and theoutermost section of the corrugated strip 126 to more tightly secure thecorrugated strip 126 inside the peripheral wall 128. The end piece 138is disposed at an end of the heater element 122 so that the end of thecorrugated strip 126 disposed proximate the center of the outer may besecured to the end piece 138.

According to the present disclosure, the heating apparatus has theadvantages of providing more power in a smaller area, thereby reducingthe size and weight of the heating apparatus without compromising heaterdurability. The heating apparatus can provide a relatively fasterheat-up during engine cold start and during transient conditions.

Additionally, the supports as described herein may be arranged in orderto block what is known as a “view factor,” or a line of sight betweenparts that could radiate heat to each other. The supports may bearranged to block a direct line of sight between heating elements orportions of the same heating element to create a line of sight to acooler support. Such arrangements should be construed as falling withinthe scope of the present disclosure.

While the heating apparatus has been described to include cartridgeheater, a tubular heater or a cable heater, it should be understood thatthe teachings of the present disclosure may be applied to other types ofheaters without departing from the scope of the present disclosure.

It should be noted that the disclosure is not limited to the embodimentdescribed and illustrated as examples. A large variety of modificationshave been described and more are part of the knowledge of the personskilled in the art. For example, the application of exhaust heating ismerely exemplary and thus any heating application with a fluid flow in afluid conduit should be construed as being within the scope of thepresent disclosure. These and further modifications as well as anyreplacement by technical equivalents may be added to the description andfigures, without leaving the scope of the protection of the disclosureand of the present patent.

What is claimed is:
 1. An exhaust gas heating unit for an exhaust systemof an internal combustion engine, the exhaust gas heating unitcomprising: a tubular housing comprising an outer peripheral walldefining a tubular shape and having an interior hollow space; and aheating element that has a first end and a second end and extendslongitudinally between the first end and the second end to form a spiralshape within the interior hollow space, wherein the heating elementcomprises: an external sheath, the external sheath formed of a thermallyconductive material; an electrically conductive resistance element thatextends longitudinally within the external sheath; and electricallyinsulating material disposed about the resistance element between theresistance element and the sheath; and a heat transfer member positionedwithin the interior hollow space, the heat transfer member being formedfrom one or more strips of thermally conductive material, wherein theone or more strips contact the external sheath at a plurality oflocations between the first end and the second end, and wherein the heattransfer member has a corrugated shape that follows the spiral shape ofthe heating element.
 2. The exhaust gas heating unit according to claim1, wherein the first end is connected to a first power pin and thesecond end is connected to a second power pin.
 3. The exhaust gasheating unit according to claim 2, wherein the first and second powerpins extend outside the interior hollow space of the tubular housing. 4.The exhaust gas heating unit according to claim 1, wherein a firstsection of the at least one strip is positioned radially outward of asecond section of the at least one strip, the second section beingfurther along the spiral shape than the first section.
 5. The exhaustgas heating unit according to claim 1 further comprising a spacerdisposed in a gap that is radially between the heat transfer member andthe tubular housing.
 6. The exhaust gas heating unit according to claim5, wherein the spacer is configured to inhibit exhaust gas flow throughthe gap.
 7. The exhaust gas heating unit according to claim 1 furthercomprising an end piece disposed at the second end proximate a center ofthe interior hollow space.
 8. The exhaust gas heating unit according toclaim 7, wherein the heat transfer member is secured to the end piece.9. The exhaust gas heating unit according to claim 1, wherein theexternal sheath is configured to loosely contact the at least one strip.10. The exhaust gas heating unit according to claim 1, wherein the atleast one strip is fixed to the external sheath at the plurality oflocations.
 11. The exhaust gas heating unit according to claim 1,wherein the plurality of locations are spaced at a spacing along alength of the strip, wherein the spacing is less than ten times anoutside diameter of the external sheath.
 12. The exhaust gas heatingunit according to claim 11, wherein a natural frequency of vibration forsections of the heater element between adjacent two locations of theplurality of locations is greater than 400 Hz.
 13. The exhaust gasheating unit according to claim 1, wherein the at least one stripincludes a single strip that follows the spiral path from the second endproximate a center of the interior hollow space to the first endproximate the outer peripheral wall.
 14. An exhaust gas heating unit foran exhaust system of an internal combustion engine, the exhaust gasheating unit comprising: a tubular housing comprising an outerperipheral wall defining a tubular shape and having an interior hollowspace; and a heating element that has a first end proximate the outerperipheral wall and a second end proximate a center of the interiorhollow space, the heating element extending longitudinally between thefirst end and the second end along a spiral path within the interiorhollow space, wherein the heating element comprises: an external sheath,the external sheath formed of a thermally conductive material; anelectrically conductive resistance element that extends longitudinallywithin the external sheath; and electrically insulating materialdisposed about the resistance element between the resistance element andthe sheath; and a heat transfer member positioned within the interiorhollow space, the heat transfer member being formed from one or morestrips of thermally conductive material, wherein the one or more stripsare coupled to the external sheath at a plurality of locations betweenthe first end and the second end, and wherein the heat transfer memberhas a shape that follows the spiral shape of the heating element andincludes a plurality of substantially “V-shaped” segments, each V-shapedsegment is associated with a bent portion of the one or more strips. 15.The exhaust gas heating unit according to claim 14 further comprising anend piece disposed at the second end and secured to the heat transfermember.
 16. The exhaust gas heating unit according to claim 14, whereinthe heat transfer member is coupled to the external sheath, at least inpart, through a frictional engagement.
 17. The exhaust gas heating unitaccording to claim 14 further comprising a spacer disposed in a gap thatis radially between an outermost section of the heat transfer member andthe tubular housing, the spacer being configured to inhibit exhaust gasflow through the gap.
 18. The exhaust gas heating unit according toclaim 14, wherein a natural frequency of vibration for sections of theheater element between adjacent two locations of the plurality oflocations is greater than 400 Hz.
 19. An exhaust gas heating unit for anexhaust system of an internal combustion engine, the exhaust gas heatingunit comprising: a tubular housing comprising an outer peripheral walldefining a tubular shape and having an interior hollow space; and aheating element that has a first end proximate the outer peripheral walland a second end proximate a center of the interior hollow space, theheating element extending longitudinally between the first end and thesecond end along a spiral path within the interior hollow space, whereinthe heating element comprises: an external sheath, the external sheathformed of a thermally conductive material; an electrically conductiveresistance element that extends longitudinally within the externalsheath; and electrically insulating material disposed about theresistance element between the resistance element and the sheath; a heattransfer member positioned within the interior hollow space, the heattransfer member being formed from one or more strips of thermallyconductive material; and a spacer disposed in a gap that is radiallybetween an outermost section of the heat transfer member and the tubularhousing, the spacer being configured to inhibit exhaust gas flow throughthe gap, wherein the one or more strips are fixed to the external sheathat a plurality of locations between the first end and the second end,wherein the heat transfer member has a corrugated shape that follows thespiral shape of the heating element, and wherein the first end isconnected to a first power pin and the second end is connected to asecond power pin, the first and second power pins extending outside theinterior hollow space of the tubular housing.
 20. The exhaust gasheating unit according to claim 19 further comprising an end piecedisposed at the second end and secured to the heat transfer member.